Mount Sinai was completely enveloped in smoke, because the LORD had descended on it in fire. And the smoke rose like the smoke of a furnace, and the whole mountain quaked violently.
Jewish Publication Society of America Version (JPS1917) - Exodus 19:18 >Now mount Sinai was altogether on smoke, because the LORD descended upon it in fire; and the smoke thereof ascended as the smoke of a furnace, and the whole mount quaked greatly.